The majority of loads to be driven by electronic devices are designed so as to present impedances consistent with low-cost semiconductor devices. This implies operation at readily available voltage or current sources. Resistive and low-reactance loads therefore present no challenge to conventional drive techniques.
Highly reactive loads and loads with inconstant impedances, such as gas tubes or motors, sometimes however require voltages or currents for transient behavior which are totally inconsistent with those required for later static operation. Multiple energy sources with entirely disparate characteristics are therefore required for tightly-controlled transient behavior.
Controlled magnetic core saturation to form switches or amplifiers of inductive components has been in use for many years to inexpensively drive large and/or unusual electrical loads. Current examples of these approaches include U.S. Pat. No. 7,706,424—‘Gas discharge laser system electrodes and power supply for delivering electrical energy to same’, #7,675,761—‘Method and apparatus to control two regulated outputs of a flyback power supply’, and #7,675,242—‘Electronic ballast’. Prior art furnishes many examples of single-path control using magnetic components, but does not teach inexpensive control of multiple energy sources within a single device.
Highly inductive motors belong to a class of devices which initially require high winding voltage in order to quickly develop magnetic flux, but subsequently require high current at low voltage to perform work. Common practice of operating motors within the fixed voltage range of a power supply therefore forces a compromise between allowable winding inductance and transient response. Low inductance, however, exacerbates ohmic losses in high power applications where drive current must be increased to maintain output power requirements. A burgeoning application encountering these obstacles is found in electrically-powered transportation vehicles, the motors for which typically have compromised torque curves in order to meet system voltage constraints.
This category of loads therefore is much more expensive to drive quickly than more pedestrian loads, in that requisite drive circuitry often must be doubled to achieve dual voltage and current requirements. The use of semiconductors in the high-voltage path or multiple controlled reactors as well increases cost, in that high-voltage production processes are more expensive than processes for lower voltages. A need exists for a method and apparatus whereby loads of unusual or inconstant impedance may be inexpensively driven without degrading system transient performance.